An air spring is used as a secondary spring, which is one of the spring devices provided on a railway truck of a railway vehicle and is placed between the railway truck and the vehicle body. For example, a bolsterless railway truck frequently incorporates an air spring having a structure in which a diaphragm and a stopper rubber are combined. The air spring attenuates vertical vibrations of the vehicle body. Although, the air spring having the foregoing structure has a nonlinear spring constant in the vertical direction and consequently exhibits excellent vibration-absorbing ability, it has a nearly linear spring constant in the horizontal direction and consequently exhibits poor ability to prevent the horizontal relative movement between the railway truck and the vehicle body. As a result, when a high-speed running of a vehicle is intended without changing the existing railway track, at the time of the curved-track running, a lack of cant causes a centrifugal force exceeding a predetermined limit, thereby increasing the amount of the horizontal (leftward and rightward) relative movement between the railway truck and the underframe of the vehicle. It has been recognized that this increase creates significant rolling of the vehicle and collisions of the underframe with the leftward-and-rightward-movement stopper, thereby impairing the comfortableness in the running vehicle.
To solve this problem, in particular, for such a use as in a railway vehicle intended to perform high-speed running, an air spring is used that has a nonlinear property achieved by limiting the leftward-and-rightward movement of the stopper rubber with respect to the vehicle. At the time of the straight-track running, the foregoing air spring functions as a relatively flexible spring having a spring constant obtained by combining the properties of the diaphragm and the stopper rubber. At the time of the curved-track running or the like, when a leftward-and-rightward displacement exceeding a predetermined amount is created, the deformation of the stopper rubber is restricted and only the diaphragm functions as the spring, thereby giving the air spring a large spring constant. Such an air spring has been disclosed, for example, in Patent Literature 1.